Device for generating a fixture

ABSTRACT

A device is provided which is capable of generating a surface that at least partially conforms to the contour of an article. The surface is defined by the ends of a number of threaded members which are supported within a suitable support structure. The threaded members are aligned so as to be substantially parallel to and threadably engaged with each other. As a result, rotation of an individual threaded member will cause that threaded member to be longitudinally moved relative to its adjacent threaded members and the support structure, without displacing an adjacent threaded member. The surface can be readily configured manually or automatically to serve as a die or mold cavity when the entire surface has been generated to conform to the entire contour of the article. Alternatively, the surface can be generated so as to provide a suitable fixture surface for supporting and securing a workpiece during a machining or welding operation. Due to its method of generation, the surface can be quickly and repeatedly reconfigured to conform to an article or workpiece having a completely different contour.

This is a division of application Ser. No. 08/009,703, filed Jan. 27,1993 now U.S. Pat. No. 5,513,972.

The present invention generally relates to equipment used in theproduction and processing of manufactured articles and components. Moreparticularly, this invention relates to a surface generating devicewhich can be readily configured to form the surface of a die, mold orfixture, wherein the surface generating device can be quickly andaccurately configured so as to be particularly suitable for producingprototype or short-run production components.

BACKGROUND OF THE INVENTION

Modern manufacturing and prototype operations have created a demand formanufacturing equipment which can be readily produced and assembled forthe purpose of producing prototype and short-run components by variousmethods. As a particular example, current computer-aided design andmanufacturing technology which is employed to develop dies used in metalforming processes often rely on computer simulations of the particularmetal forming process to reduce the design time and tooling costs forthe die, as well as the time necessary to verify the design of the die.The quality of the finished die directly impacts the quality of thearticle produced. Thus, a rapidly produced die of lesser quality mayresult in additional time and costs to finish the article, whichtherefore increases the overall time and cost required to produce afinished article. Consequently, dies which are rapidly designed to beeconomical for use in prototype and short production runs are oftenachieved as a trade-off in die quality and life.

Nonetheless, much attention has been devoted to the development ofprocesses for the rapid manufacturing of dies, particularly draw diesused in stamping operations. The benefits associated with rapidlyproduced draw dies are apparent. As an example, lower cost dies offer amanufacturer the opportunity to compete in niche or limited volumemarkets. In addition, the ability to rapidly obtain a draw die whendeveloping a process facilitates the ability to have a component readyfor prototype assembly, while also subsequently facilitating theproduction line die design.

However, rapidly produced dies have a significant disadvantage, in thatsuch dies can be more readily made if produced from materials which aresofter than the conventional cast iron used. In particular, this issueis paramount when attempting to obtain "cast-to-size" dies, whichgenerally employ plastics or other less durable materials which have alower melting point than cast iron. As a result, the durability ofrapidly produced dies is often inferior to that of conventional dies,such that some limitation must be placed on the volume of parts producedfrom the die before the die requires reworking or reconstruction.

A suggested alternative to conventional methods of die making has beenthe use of an assembly of hard metal rods or pins which are frictionallyheld together by a suitable frame member. The hard metal rods provide amore durable die surface than the materials typically used forrapidly-produced dies, such as those noted above. An obviousdisadvantage is that the die surface will not be smooth. However, a lessobvious disadvantage associated with the use of the rods is that ofachieving accurate rod placement. One approach is to use a reverse modelof the desired surface. However, this approach negates much of the timeadvantage sought by seeking a rapidly-produced die, since forming asuitable model is often time consuming and costly.

To alleviate the need for a model, it has been suggested to useelectromechanical drives and sensors to position the rods to theirassigned positions based on known surface data for the article to beproduced. However, the friction between adjacent rods which serves tokeep each rod in its proper place also tends to dislodge adjacent rodswhile an individual rod is being positioned. If all of the rods arebeing positioned simultaneously to overcome this drawback, the driverand sensor system tends to be much too complex for a die of anysignificant size.

Thus, it would be desirable to provide a die which could be rapidlyproduced, assembled and adapted for a particular use in a minimal amountof time, so as to be particularly suitable for use in manufacturingprototype and short-run components. The above discussion is alsoapplicable to the making of molds for molding processes, such as forplastic molding and die casting operations, as well as for othermanufacturing processes, such as machining and welding operations, whichhave conventionally required different solutions. Similar to thesituation described above for dies, modem manufacturing and prototypeoperations have created a demand for fixtures which can be readilyproduced and adapted for the purpose of producing prototype andshort-run components by various machining and joining methods. Alsosimilar to dies, the ability to rapidly produce a fixture having theproper dimensional characteristics for a given component becomes ofgreat importance, particularly for prototype and short-run articles,wherein the time and costs required to produce the necessary fixturesrepresents a significant proportion of the total manufacturing time andcosts for the article to be produced.

Fixturing irregularly-shaped parts is often quite tedious, particularlywhere the article being fixtured does not have suitably rigid locationsfor restraining the article, such that the article tends to be distortedby the forces generated by the fixture to secure the article. Customizedfixturing is often required to properly support, locate and clamp sucharticles, resulting in fixtures that are both time consuming and costlyto produce. Again, such fixturing is not an economical option whenprototype or short-run production is the goal, particularly in view ofthe fact that a specially configured fixture will most likely beunsuitable for use with any other article.

Thus, as stated previously, it would be desirable to providemanufacturing equipment, such as dies, molds and fixtures, which couldbe rapidly produced, assembled and adapted for a particular use in aminimal amount of time, so as to be particularly suitable for use inmanufacturing prototype and short-run components. Such rapidly-produceddies and molds would only be feasible if they could be readily andaccurately produced, such that the time necessary to develop the diesand molds was minimized. Suitable rapidly-produced fixtures wouldpreferably be readily adaptable and reconfigurable so as to locate,support, and clamp components having various geometries and shapes, suchthat the fixtures would be reusable and therefore economical for use inmanufacturing prototype and short-run components.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a surface generating devicewhich can be configured so as to at least partially conform to thecontour of an article to be formed or worked.

It is a further object of this invention that such a device be capableof generating a surface which is suitable for use as a die, mold orfixture in manufacturing and processing operations.

Lastly, it is yet another object of this invention that such a device beconstructed of a number of aligned elements which can be individuallypositioned without adversely effecting the position of adjacentelements, such that the surface defined by the ends of the elements canbe readily modified by longitudinally positioning one or more of theelements, and wherein the surface can be configured to define a die ormold cavity which closely conforms to the desired contours of anarticle, or a fixture capable of supporting, locating and clamping acomponent for machining or joining operations.

In accordance with a preferred embodiment of this invention, these andother objects and advantages are accomplished as follows.

According to the present invention, there is provided a device capableof generating a surface which can be configured to at least partiallyconform to the contour of an article. The surface is defined by the endsof a number of threaded members which are supported within a supportstructure. The threaded members are oriented within the supportstructure so as to be substantially parallel to and threadably engagedwith each other. As a result, rotation of an individual threaded memberwill cause that threaded member to be longitudinally moved relative toits adjacent threaded members and the support structure, withoutimposing rotation on its adjacent threaded members.

Appropriate longitudinal positioning of each of the threaded members canbe performed such that at least a portion of the surface, as defined bythe ends of the threaded members, will conform to at least a portion ofthe contour of the article. As a result, the type of surface featurespossible with the surface generating device of this invention is onlylimited by the number and diameter of the threaded members used. Forexample, generating a very intricate and contoured surface would requirea large number of threaded members having relatively small diameters toimprove the resolution of the surface.

Furthermore, the surface can be quickly generated by simply assemblingthe desired number of the threaded members within a suitable supportstructure, and then rotating each threaded member a sufficient number oftimes to properly locate each threaded member according to therequirements of the particular article being formed or worked. Where anarticle has been designed by computer-aided design and manufacturingmethods, the dimensional data produced by such methods can be readilyused to position the threaded members in an automated manner.

When the entire surface has been generated to conform to the entirecontour of the article, the surface can be used as a die cavity or amold cavity. When used as a die or mold to form intricate articlesrequiring high surface quality, a metal layer can be deposited on theends of the threaded members so as to form a more uniform die or moldsurface. If used as a mold, some of the threaded members can be producedwith reduced diameter portions at predetermined locations along theirlength to create passages through the mold.

Alternatively, the surface can be generated so as to provide a suitablefixture surface for supporting a component intended to be machined,welded or the like. As noted before, if the component has been designedby computer-aided design and manufacturing methods, the dimensional dataproduced by such methods can be readily used to position the threadedmembers in an automated manner to properly support the component on thesurface, as well as to properly locate and clamp the component to thesurface. In particular, some of the threaded members can be modified soas to serve as stop pins, locating pins or clamps. After a production orprototype run, the fixture can be readily reconfigured to secure andsupport a component having a completely different contour than thefirst.

Other objects and advantages of this invention will be betterappreciated from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of this invention will become moreapparent from the following description taken in conjunction with theaccompanying drawing wherein:

FIG. 1 is a side view of a surface generating device composed of anumber of threaded rods in accordance with this invention;

FIG. 2 is an end view of the surface generating device of FIG. 1;

FIG. 3 shows a manual clamp secured to the surface generating device ofthis invention;

FIG. 4 shows a stop insert mounted to a threaded rod in accordance witha particular aspect of this invention;

FIG. 5 shows a locating insert mounted to a threaded rod in accordancewith a particular aspect of this invention;

FIGS. 6a and 6b show an automated clamp insert mounted to a threaded rodin accordance with a particular aspect of this invention;

FIG. 7 illustrates a preferred arrangement of stop, locating andclamping inserts in accordance with this invention;

FIG. 8 illustrates a device for actuating the automated clamp inserts ofFIGS. 6a and 6b in accordance with this invention;

FIG. 9 shows threaded rods having reduced diameter portions for creatingpassages through the surface generating device in accordance with thisinvention;

FIG. 10 is a plan view of an irregular flowpath through the surfacegenerating device formed by reduced diameter portions on a series ofthreaded rods; and

FIG. 11 is a side view of the irregular flowpath through the surfacegenerating device of FIG. 10 in relation to the mold surface which isdefined by the threaded rods.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with this invention, a surface generating device isprovided that is capable of generating a surface which at leastpartially conforms to the contour of an article. The surface can bereadily configured manually or automatically through the use ofdimensional data provided by computer-aided design and manufacturingmethods. The surface, referred to as a composite surface in the sensethat it is composed of numerous individual elements, can be used as adie or mold cavity when the entire composite surface has been generatedto conform to the entire contour of the article. Alternatively, thecomposite surface can be generated so as to provide a suitable fixturesurface for supporting and securing the article while work is performedon the article, such as machining or welding. Due to its method ofgeneration, the surface can be later reconfigured to conform to anarticle having a completely different contour.

Shown in FIGS. 1 and 2 is a surface generating device 10 in accordancewith this invention. The surface generating device 10 includes a supportstructure, such as the holding frame 14 shown. The construction of theholding frame 14 can vary widely, according to the intended function ofthe surface generating device 10. In FIGS. 1 and 2, the holding frame 14is a pair of frame halves held together by a pair of screws 20, thoughother means for securing the holding frame 14 together could be readilyemployed by one skilled in the art. The holding frame 14 defines aninterior surface which restrains a number of threaded rods 12 within theholding frame 14. A composite surface 16 is generated by the ends 32 ofthe threaded rods 12. The composite surface 16 can be configured, andreconfigured as will be explained below, to form, in accordance with afirst embodiment, a draw die member 17 as shown in FIGS. 1 and 2, or amold member in accordance with a second embodiment shown in FIGS. 9through 11, or a fixture in accordance with a third embodiment shown inFIGS. 3 through 8, all of which will be discussed in detail below. Forpurposes of convenience, the surface generating device 10 is illustratedas including relatively few threaded rods 12 but, as will become evidentby the discussion below, the size of the surface generating device 10and its associated composite surface 16 can vary significantly dependingon the particular application.

The threaded rods 12 can be formed from any suitable material whichexhibits the required durability and temperature capability for theintended process, while also being sufficiently formable and/ormachinable to permit the formation of threads 30. Most often, rodsformed from an appropriate steel will be most suitable, with theparticular grade of steel being decided on the basis of trade-offsbetween mechanical properties, ease of machining, cost and hardness,however other suitable materials could also be employed depending on theparticular application and requirements.

As seen in FIG. 1, the threaded rods 12 are supported by the holdingframe 14 such that they are oriented to be substantially parallel toeach other. In addition, male threads 30 and female threads 31 of thesame pitch and pitch diameter are formed on each of the threaded rods 12and on parallel semi-cylindrical channels formed in the interior surfaceof the holding frame 14, respectively, such that the threaded rods 12are threadably engagable with each adjacent threaded rod 12 as well asthe interior surface of the holding frame 14, when applicable. As aresult, rotation of an individual threaded rod 12 will cause only thatthreaded rod 12 to be longitudinally moved relative to its adjacentthreaded rods 12 and the holding frame 14, without imposing rotation on,and therefore longitudinal movement of, the adjacent threaded rods 12.

Rotation of each threaded rod 12 is preferably achieved through asuitable feature formed on the end 34 of each threaded rod 12 oppositethe end 32 defining the composite surface 32. As shown, the feature is aslot which permits the manual use of a flathead screwdriver to rotateeach threaded rod 12, although other means known in the art could alsobe used to effect the rotation. An automatic screwdriver system 18 isschematically illustrated to indicate the capability of automating thegeneration of the composite surface 16 through computer-controlledautomation made possible by dimensional data from computer-aided designand manufacturing methods.

To facilitate automated generation of the composite surface 16, theautomatic screwdriver system 18 is preferably adapted to be able toreadily engage an arbitrarily positioned threaded rod 12 despite minoruncertainties in its position. A slotted head with a half-ramp form,such as those found on tamper-proof screws, would meet this requirement,but would permit only unidirectional positioning of the threaded rods12. Where a bi-directional capability is desired or necessary, theslotted ends 34 of the threaded rods 12 could instead be provided withradial serrations or some other irregular form to positively engage amating surface on the automatic screwdriver system 18 from any relativeposition. If desired, engagement could be further enhanced through theuse of magnetic forces, as in an electromagnetic clutch.

For use as a draw die 17 in accordance with the first embodiment of thisinvention, it is preferable that the threaded rods 12 be of the samelength. It is also preferable that the threaded rods 12 each have asufficient thread height to minimize the voids between adjacent threadedrods 12, so as to maximize the packing density of the threaded rods 12.To achieve this goal, the ratio of the thread height H of each threadedrod 12 to the outside diameter D of each threaded rod 12 must be atleast about 0.134 according to the formula:

    H/D ≧1- cos 30°

With an H/D ratio of at least about 0.134, the threaded rods 12 will besufficiently densely packed such that no voids will be present betweenany group of three threaded rods 12, as illustrated in FIG. 2. Thiscondition can be satisfied for American Standard coarse threads of up to0.5 inch in diameter. For threaded rods 12 having larger diameters, anonstandard thread height H would be required. For purposes ofgenerating a composite surface 16 suitable for die and moldingprocesses, it would not be expected that threaded rods 12 havingdiameters in excess of 0.5 inch would be required, in that smallerdiameter threaded rods 12 would enable higher surface resolution, andwould thus enable more detailed contouring of the composite surface 16.

Furthermore, many applications will require that the ends 32 of thethreaded rods 12 be bonded or otherwise permanently joined together toform a more durable and uniform composite surface 16, particularly wherea highly uniform die or mold surface is required, such that articlesproduced will have a high quality surface finish. An additional benefitwhich can be realized by joining the ends 32 of the threaded rods 12together is to substantially eliminate all voids between the threadedrods 12, such that the composite surface 16 is fluid-tight. One suitablemethod for joining the ends 32 of the threaded rods 12 together is toprecoat the threaded rods 12 with a material, such as zinc, tin orcopper, as well as other materials known to those skilled in the art.After assembling the threaded rods 12 in the holding frame 14, thesurface generating device 10 is heated to melt the coating and therebyfuse the threaded rods 12 together. Thereafter, the composite surface 16can be machined to achieve the desired surface quality. Alternatively, ametal layer 90 (see FIG. 11) can be applied directly to the ends 32 ofthe threaded rods 12 to form a uniform coating. Most preferably, a metalspray electroplating process would be used to deposit the metal layer90, such that the metal layer 90 sufficiently infiltrates the voidsbetween the threaded rods 12 to a predictable depth so as to form thedesired fluid-tight composite surface 16. Suitable materials for thisprocess would be metals, such as chromium or nickel, as well as othermaterials known to those skilled in the art.

While a metallurgical (as opposed to mechanical) bond between thethreaded rods 12 and the metal layer 90 would be most effective indeveloping a high strength bond, the back surface composed of theslotted ends 34 could be machined flat and reinforced by a flat plate(not shown) to supplement the strength of the bond formed at the ends32. Accordingly, except in extremely unusual cases, a metallurgicalreaction between the threaded rods 12 and the metal layer 90 would notbe required.

However, if a strong metallurgical bond is required, then the choice ofcoating materials is restricted to materials which will react with thematerial of the threaded rods 12. On heating the die 17, the firstreaction would be the melting of the metal layer 90, then partialdissolution and liquefaction of the adjacent threaded rod material toform an alloy. The metal layer 90 would then diffuse into the threadedrods 12, resulting in a reduction in alloy surface concentration and anincrease in its melting point, followed by resolidification of thesurface. Such methods are known and within the expertise of one skilledin the art.

An approach to achieving the above while simultaneously improving themechanical properties of the die 17 would be to use low carbon steelthreaded rods 12 which have been surface carburized. Since the meltingpoint of iron carbon alloys decreases with carbon content (at least overthe range of carbon content applicable here), the carbon-rich surface ofeach threaded rod 12 would melt first. Then, as the carbon diffused intothe cores of the threaded rods 12, the melting point would increase andthe surface would resolidify in the same manner described above. Becauseof the high diffusivity of carbon in iron, heating would have to beextremely rapid to ensure that the initial concentration gradient wasmaintained during the time it took to heat the die 17 to its meltingpoint. So as to ensure that this occurs and that the temperature rise isa maximum at the threaded rod ends 32, electric resistance heatingmethods could be employed, although other techniques could also be used.

When configuring the composite surface 16 for a particular application,the positioning of the individual threaded rods 12 can be achieved withor without the use of an absolute position sensor (not shown). Startingfrom an initial state where the ends 32 of the threaded rods 12 arealigned such that the composite surface 16 is planar and substantiallynormal to the longitudinal direction of the threaded rods 12, theautomatic screwdriver system 18 can incorporate a stepper motor or abrushless motor which can quickly and precisely position each threadedrod 12 simply by counting the number of angular steps made by the motor.For example, a 0.5 inch diameter threaded rod 12 with a standard coarsethread of 13 threads per inch, driven by a stepper motor with a lowangular resolution of 12 steps per revolution, would permit positioningaccuracy of about 0.006 inch. More typical stepper resolutions of 24 and48 steps per revolution would provide positioning accuracy of 0.003 and0.0015 inch, respectively.

In its simplest form, the automatic screwdriver system 18 can be aunidirectional drive which will suffice if the threaded rods 12 aremoved only once and in one direction. Repeated reconfiguration of thesame composite surface 16 generally necessitates the use of a positionsensor in conjunction with the automatic screwdriver system 18. Theposition sensor, however, would not need to be an absolute positionsensor. A very simple spring-loaded pointer, operating off the end 32 ofeach threaded rod 12 being positioned, could be used to make and break,at some predetermined height, an electrical contact serving as a relayto the circuit powering the automatic screwdriver system 18.

An important consideration affecting the utility of the surfacegenerating device 10 is the amount of time required to generate acomposite surface 16 having a practical size and resolution. Verticalresolution of the composite surface 16 is dictated by the accuracy ofthe longitudinal positioning of the threaded rods 12, as discussedabove. Accordingly, suitable vertical resolution for many dieapplications can be achieved by properly selecting the thread pitch ofthe threaded rods 12 and/or the angular step size of the selected motordrive.

In contrast, high horizontal resolution at the composite surface 16 ismore costly, since the number of threaded rods 12 required increasesparabolically with any given linear increase in the size of thecomposite surface 16. As a result, significantly longer surfacegeneration times are required for larger composite surfaces 16 if thethreaded rods 12 are positioned sequentially and not simultaneously. Inthat simultaneous positioning would require a very complex automaticscrewdriver system 18, it is anticipated that the threaded rods 12 willbe individually positioned. For this reason, horizontal resolution willtypically be kept to a necessary minimum, i.e., threaded rods 12 havingthe largest acceptable diameter will typically be used. Reduced surfaceresolution resulting from the use of larger threaded rods 12 can bealleviated by use of the metal layer 90 as a final step to define thecomposite surface 16, as discussed above, or by machining to finalshape.

Another consideration regarding generation time of the composite surface16 is the desired shape of the composite surface 16, and morespecifically, how close the final average height of the compositesurface 16 is to its final median height (i.e., the midpoint between thehighest and the lowest point on the composite surface 16). Analytically,when starting from an initial planar composite surface 16, surfacegeneration time will be the longest for any composite surface 16 whichhas its average height equal to its median height since, in such a case,creating the surface by either extension or retraction, or a combinationthereof, of the threaded rods 12 will require the same total cumulativethreaded rod 12 movement, and thus the same amount of time. Typically,however, the desired average surface height of a draw die 17 will besignificantly above or below the median height of the composite surface16, such that retraction or extension, respectively, of the threadedrods 12 will generate the surface faster than that of the previous"worst case" scenario. In order to have the option to select either theretract or extend mode, the automatic screwdriver system 18 preferablyhas a hi-directional capability.

Where male and female halves of a die are required, the surfacegenerating device 10 of this invention can be used to simultaneouslyproduce each half if the length of the threaded rods 12 are all thesame. Specifically, by generating the desired die surface with thecomposite surface 16, a complementary surface is generated on theopposite surface defined by the slotted ends 34 of the threaded rods 12.In such a case, after fusing together both the ends 32 and the slottedends 34 of the threaded rods 12, the surface generating device 10 can becut in half, such as by electrical discharge machining, to produce amating pair of dies 17. However, a requirement for complementary maleand female molds is typically the rare exception.

In any case, once the desired composite surface 16 is generated, with orwithout fusing the threaded rod ends 32 or use of the metal plating, thedie 17 is ready for use. Accordingly, the time required to generate thecomposite surface 16, based on known dimensional data of the article tobe produced, will be substantially less than that required toconventionally manufacture a cast iron die. As a result, dies 17 madeaccording to this invention are more economical for prototype or shortproduction runs as compared to conventional east iron dies.

Alternatively, in a second embodiment of this invention, a mold suitablefor use when molding plastics or as a die casting die can also bedesigned and generated by the surface generating device 10, much thesame as the die 17 of the first embodiment. A major difference betweenthe die 17 and a mold is the material from which molds and die castingdies are conventionally formed. However, in the context of the surfacegenerating device 10 of this invention, the difference becomesinconsequential, in that the surface generating device 10 is generallyindifferent to the material chosen for the threaded rods 12 used togenerate the mold cavity.

A more fundamental issue is the necessity to provide temperature controlfor molds and dies used in both plastic molding and die castingoperations. Typically, this requirement is met by providing passages inthe mold or die which permit water or steam to flow therethrough so asto locally cool or heat, respectively, the mold or die. Conventionally,such passages are formed by drilling interconnected holes directly intothe mold or die. In terms of the present invention, it would also bepossible to drill holes into the threaded rods 12 after they areassembled and supported within the holding frame 14.

However, as shown in FIGS. 9 through 11, and according to a preferredaspect of the present invention, passages 86 can be formed within thesurface generating device 10 by providing reduced diameter portions 84on some of the threaded rods 12e prior to assembly into the holdingframe 14. Though assembly is somewhat complicated by using apredetermined arrangement of standard threaded rods 12 and "waisted"threaded rods 12e, the need for a machining operation to form thepassages 86 after assembly can be eliminated. Furthermore, as shown inFIGS. 10 and 11, the passages 86 formed can be extremely irregular,being near the surface 88 of the mold or die when desirable to promoteheating or cooling, and further away from the surface 88 when heat orcooling is not required or desired. The diameter of the passages 86 canalso be varied along a flowpath, to either increase or decrease theflowrate of the fluid through the passage 86.

The above approach can also be used to form either male or female moldor die halves, or both if the male half is the complement of the femalehalf, as discussed above in reference to the die 17. With this approach,some threaded rods 12 would have no reduced diameter portions 84, somemay have a single reduced diameter portion 84 where a passage 86 isrequired in only the male or female half, while others would have twolongitudinally spaced-apart reduced diameter portions 84 where both themale and female halves require a passage 86.

Accordingly, a significant advantage to forming the reduced diameterportions 84 prior to assembly of the threaded rods 12 and 12e in theholding frame 14 is that the reduced diameter portions 84 can belongitudinally positioned at predetermined locations on the threadedrods 12e, such that the path of the passages 86 through the surfacegenerating device 10 can vary widely, depending upon the particularrequirements of an application. Through appropriate computer modeling,the areas of a mold or die which require heating and cooling can bedetermined, as well as how efficiently the mold or die must be heated orcooled in a given region. As a result, the data generated by thecomputer model can be used appropriately to mass produce the threadedrods 12e, which can then be inserted at predetermined locations withinthe surface generating device 10. Such a capability offers theopportunity to modify flow conditions locally to the extent allowed bythe diameter of the threaded rods 12 and 12e.

In addition, individual threaded rods 12 and/or 12e can be heated usingcartridge heaters 92, shown schematically in FIG. 11, such that thepassages 86 are used for cooling only. The cartridge heaters 92 would beattached directly to selected threaded rods 12 and 12e to furtherinfluence the temperature of the mold or die cavity in the region of theselected threaded rods 12 and 12e. Because heat is transferred throughthe mold or die more readily along the length of each threaded rod 12and 12e as compared to between adjacent threaded rods 12 and 12e, thecartridge heaters 92 promote the precision by which the mold or diesurface 88 temperature can be controlled. Precise control of the mold ordie temperature can be farther promoted by independently controllingeach cartridge heater 92. In that fast response is not critical, bothtemperature sensing and control of the heating cycle of each cartridgeheater 92 would preferably be multiplexed to minimize power supply andcontroller costs.

The incorporation of passages 86 in the mold or die formed by thesurface generating device 10 creates the potential for leakage betweenthe threaded rods 12 and 12e. Furthermore, molds and dies generallyrequire better surface quality than the dies 17 of the first embodiment,such that porosity in the mold or die surface 88 created by any spacesbetween the threaded rods 12 and 12e would be unacceptable. Accordingly,in a preferred embodiment, any spaces existing between the threaded rods12 and 12e at the mold or die surface 88 must be filled.

Due to high molding temperatures typically required, particularly fordie casting dies, a preferred fill material would have a relatively highmelting point, such as copper or brass. To ensure adequate and uniformfill, vacuum infiltration techniques would preferably be used to drawthe fill material down between the threaded rods 12 and 12e. To providean even better surface finish, the ends 32 of the threaded rods 12 and12e can be chromium plated. A chromium layer, such as the metal layer 90in FIG. 11, would also maintain the chemical inertness of the mold ordie and avoid a reaction between the fill material and the material tobe molded or die cast.

As with the die 17 discussed above, a mold or die surface 88 generatedby the desired composite surface 16 would essentially be ready formediate use once an appropriate fill material and/or metal plating 90has been applied to the threaded rod ends 32. Again, the time requiredto generate the composite surface 16, based on known dimensional data ofthe article to be produced, will be substantially less than thatrequired to conventionally manufacture a mold or die casting die. As aresult, mold and dies made according to this invention will also beeconomically practical to use for prototype or short production runs.

While much of the general discussion above is also applicable tofixtures which can be formed with the surface generating device 10 ofthis invention, matters such as the surface quality generated by theends 32 of the threaded rods 12 become insignificant, as well as theneed to position each and every threaded rod 12 to closely conform tothe workpiece to be worked. However, to suitably function as a fixture,the surface generating device 10 must be equipped with specially adaptedfeatures that support, locate and securely clamp the workpiece to thefixture, particularly when an irregularly-shaped workpiece must befixtured. Thus, either more than one type of threaded rod 12 isrequired, or the threaded rods 12 must be adaptable to perform any oneof the three functions with minimal effort. The approach adopted woulddirectly effect whether the surface generating device 10 could beautomated for production rum, or require manual operation so as to belimited to prototype operations. Support, locating and clamping insertssuitable for use with the surface generating device 10 in accordancewith this invention are shown in FIGS. 3 through 8.

For both prototype (manual) and production (automated) operations, theconfiguration of the surface generating device 10 would again bepreferably established by computer-aided design and manufacturing data,similar to that for configuring the surface generating device 10 for useas a mold or die. Such information could then be used to locate theworkpiece relative to the threaded rods 12 so as to properly nest theworkpiece for optimal support. Again, an advantage with the surfacegenerating device 10 of this invention is the ability to freely rotateand reposition each individual threaded rod 12 without affecting thepositions of the neighboring threaded rods 12.

In addition, for purposes of use as a fixture, certain threaded rods 12can be selected to support the workpiece at predetermined locations,while others can be selected to horizontally locate the workpiece on thefixture surface generated by the threaded rods 12, and yet others can beselected to be equipped with clamping devices to secure the workpiece tothe surface generating device 10. A preferred fixturing surface 78 isillustrated in FIG. 7, wherein support threaded rods 12b, locatingthreaded rods 12c, and clamping threaded rods 12d are positioned on thefixturing surface 78 such that the clamping threaded rods 12d define astar-shaped pattern. Such a layout is preferred in that it would beexpected to accommodate a greater variety of workpieces. The preferredconstruction of each of these threaded rod versions will be describedmore fully below.

For purposes of automation, the automatic screwdriver system 18 proposedfor the molds and dies of the first and second embodiments is even moreproficient for generating the fixturing surface 78, in that fewerthreaded rods 12 need to be positioned to support a workpiece incomparison to generating an entire surface for use as a die 17 or moldsurface 88.

However, for reconfiguring the surface generating device 10 to fixture asecond workpiece having a geometry unlike a first workpiece, the methodof positioning the threaded rods 12 must be altered, in that thethreaded rods 12 are not initially aligned such that their ends 32 forma planar fixturing surface 78. Though stepper motors and brashlessmotors could be used to make very accurate adjustments from onefixturing orientation to another, the cumulative errors after a seriesof reconfigurations would quickly result in unacceptably largepositional errors for the threaded rods 12. One solution is tocompletely align the threaded rods 12 prior to the composite surface 16being reconfigured for the next workpiece. Alternatively, a positionsensor of the type described previously could be used in conjunctionwith the automatic screwdriver system 18 to permit absolute positioningof the threaded rods 12, regardless of their initial longitudinalpositions. The preferred choice between the above alternatives isdetermined in part by the particular requirements of the application,such as cost and desired accuracy.

Referring to FIG. 3, a manual clamp 24 is shown which is suitable forfixturing a prototype workpiece 22. As shown, the threaded rods 12 arepreferably hollowed threaded rods 12a having a longitudinal bore 52. Ina preferred embodiment of this invention, the bore 52 is sized toreceive and secure a stop insert 36 (FIG. 4), a guidepin insert 44 (FIG.5) or a clamp insert 24 or 62 (FIGS. 3, 6a and 6b).

For prototype fixturing, the manual clamp 24 preferably has at least twopins 28 which are spaced apart so as to be simultaneously insertableinto two bores 52. The pins 28 preferably extend through eachcorresponding threaded rod 12a and are secured to the threaded rods 12aby any suitable device, such as nuts (not shown) threaded onto the pins28 adjacent the slotted ends 34 of the threaded rods 12a. By using twopins 28, the manual clamp 24 is prevented from rotating as it is beingsecured to the threaded rods 12a. As shown, an adjustment screw 26 isprovided to make the actual contact with the workpiece 22, if necessary.As with the manner in which the manual clamp 24 must be secured to thethreaded rods 12a, the adjustment screw 26 is suitable only for manualfixturing adjustments made for prototype operations.

As shown in FIGS. 4 and 5, the hollow threaded rods used to receive andsecure the stop inserts 36 and the guidepin inserts 44 are designated asthreaded rods 12b and 12c. The stop inserts 36 and the guidepin inserts44 support and locate, respectively, the workpiece 22 on the surfacegenerating device 10. However, in contrast to the threaded rods 12adescribed above for the manual clamp 24, the threaded rods 12b and 12care suitable for both manual and automated operations.

With reference to FIG. 4, the threaded rods 12b adapted for use tosupport the workpiece 22 have an internal thread 46 formed on the bore52. The internal thread 46 threadably engages an external thread 40formed on the stop insert 36, here illustrated as an eccentric stop.Similar to the threaded rod 12b, the stop insert 36 is also providedwith a drive slot 42 which can be used to rotate, and thuslongitudinally position, the stop insert 36 either by a hand-heldscrewdriver, the same automatic screwdriver system 18 described abovefor positioning the threaded rods 12c, or an independent adjustingdevice which is concentric with the automatic screwdriver system 18. Toprevent machining vibrations from altering the position of the stopinsert 36, an O-ring 38, or other suitable restraining device, can bepositioned between the bore 52 and the stop insert 36 so as to providefrictional resistance to rotation of the stop 36. The O-ring 38 alsoserves to prevent swarf from contaminating the threads 40 and 46 duringa machining operation.

Generally the above description is also true for the threaded rod 12c,illustrated in FIG. 5, for horizontally locating the workpiece 22 on thesurface generating device 10. However, the guidepin insert 44 ispreferably conical so as to allow the longitudinal position of theguidepin insert 44 within the threaded rod 12c to adapt to the size ofthe hole in the workpiece 22 into which the guidepin insert 44 isintended to fit. Again, the guidepin insert 44 is furnished withexternal threads 48 which engage internal threads 46 formed on the bore52 of the threaded rod 12c. The guidepin insert 44 is also provided witha drive slot 50 which can be used to rotate, and thus longitudinallyposition, the guidepin insert 44 either by a hand-held screwdriver, theautomatic screwdriver system 18, or an independent adjusting deviceoperating concentrically with the automatic screwdriver system 18.

The similarities between the threaded rods 12a, 12b and 12c permit, in amanual operation, the manual clamps 24, stop inserts 36 and guidepininserts 44 to be interchangeable. As a result, each fixturing surface 78could be configured on a case-by-case basis, with the only requirementbeing that a surface on or locating hole in the workpiece 22 be locatedover a threaded rod 12a, 12b or 12c such that the appropriate stopinsert 36 or guidepin insert 44 engages the surface or hole.

In an automated system, the primary difference is that the stop inserts36 and guidepin inserts 44 must be permanently located on the fixturesurface 78 to facilitate automatic operation of the fixture. Inaddition, the mechanism by which the workpiece 22 is clamped to thesurface generating device 10 must allow automation. As noted above, thefixture surface 78 shown in FIG. 7 is suitable for a wide variety ofworkpieces 22 within a given size range, and therefore serves as apreferred arrangement for the threaded rods 12b and 12c on the surfacegenerating device 10 when used as a fixture. Though it may be necessaryto arrange the stop inserts 36 and guidepin inserts 44 to bepart-specific, the structural similarities between the threaded rods12band 12c permit the stop inserts 36 and guidepin inserts 44 to beinterchangeable between the threaded rods 12b and 12c, so as to allowthe stop inserts 36 and guidepin inserts 44 to be quickly relocated onthe fixturing surface 78. Otherwise, automated interchanging of thethreaded rods 12b and 12c is also feasible using techniques analogous tothe automatic screwdriver system 18, particularly in view of therelatively few stop inserts 36 and guidepin inserts 44 required for agiven fixturing application.

A preferred approach to automating the clamping function of the surfacegenerating device 10 is shown in FIGS. 6a and 6b. The preferredautomated clamping mechanism includes a hollow threaded rod, denoted asthreaded rod 12d, and concentrically mounted upper and lower clampinserts 58 and 60, respectively. Similar to the stop inserts 36 andguidepin inserts 44, the lower clamp insert 60 is provided with externalthreads 70 which threadably engage the internal threads 46 formed on thebore 52 of the threaded rod 12d. Furthermore, the lower clamp insert 60is provided with a drive slot 66. Again, the lower clamp insert 60 canbe rotated either by hand or with an automated device such as theautomatic screwdriver system 18, such that the lower clamp insert 60 canbe longitudinally positioned within the threaded rod 12d.

At its upper end, the lower clamp insert 60 has a peripheral slot 74into which a flange 72 extends radially inward from the upper clampinsert 58. As such, the upper and lower damp inserts 58 and 60 arepermanently secured together while permitting relative rotation betweenthe two. The upper clamp insert 58 is not provided with threads, butinstead has a key 56 which follows a key slot 54 formed in the bore 52of the threaded rod 12d. As a result, the upper clamp insert 58 isprevented from rotating, such that orientation of the upper clamp insert58 is determined by the angular position of the threaded rod 12d and notthe lower clamp insert 60. As such, the upper and lower clamp inserts 58and 60 can be raised and lowered relative to the threaded rod 12dwithout affecting the orientation of a clamping arm 62 mounted on theupper clamp insert 58. Preferably, the slotted end 34 of the threadedrod 12d is asymmetrical (e.g., one half of the slot is larger than thediametrically opposed half of the slot) in a manner which corresponds tothe orientation of the clamping arm 62, such that the orientation of theclamping arm 62 is known based on the angular position of the asymmetricslotted end 34.

The clamping arm 62 is secured to the upper clamp insert 58 with a pivotpin 68, and is actuated by an actuator rod 64 which extends through boththe upper and lower clamp inserts 58 and 60. FIG. 6a illustrates theclamping arm 62 in a deployed position, in which extension of theactuator rod 64 imposes a clamping force through the clamping arm 62 tothe workpiece (not shown). FIG. 6b illustrates the clamping arm 62 in astowed position, wherein both the upper clamp insert 58 and the actuatorrod 64 have been retracted. The actuator rod 64 is preferably retractedsufficiently to pivot the end of the clamping arm 62 adjacent the pivot68 into a cavity 76 formed in the upper clamp insert 58. Furtherretraction of the upper and lower clamp inserts 58 and 60 allow theclamping arm 62 to be completely stowed within the threaded rod 12d.

As shown in FIG. 8, a suitable actuation system for a number of actuatorrods 64 is to provide a driver plate 80 formed by a second surfacegenerating device 10. The drive plate 80 is configured with a threadedrod 82 designated for each clamping arm 62. An actuator rod 64 isrigidly attached to each threaded rod 82 to actuate each of the clampingarms 62. By raising and lowering the driver plate 80, the clamping arms62 of each of the threaded rods 12d are actuated to simultaneouslyengage and disengage, respectively, the workpiece 22. However, it isforeseeable that the clamping arms 62 might preferably be actuatedindividually with dedicated actuating cylinders or solenoids.

From the above description of the surface generating device 10 in termsof providing a fixturing surface 78, the process of configuring thesurface generating device 10 is generally as follow. First, from thedrawings and process plan for a given workpiece or part, thelongitudinal position of each threaded rod 12a through 12d isdetermined. If manual operation is required, the manual clamps 24, stopinserts 36 and guidepin inserts 44 are manually mounted in theirrespective threaded rods 12a, 12b and 12c, and longitudinally positionedaccording to the workpiece's drawing requirements to generate therequired fixture surface 78. If an automated operation is used, thenecessary height of each required threaded rod 12a through 12d and theircorresponding stop inserts 36, guidepin inserts 44 and clamp arms 62 isprogrammed into the automatic screwdriver system 18, and the appropriatefixture surface 78 is automatically generated. The surface generatingdevice 10 is then loaded into the machining or welding center, etc., forimmediate use. In the automated system, the fixture surface 78 can beautomatically reconfigured if necessary or desirable, while the manualsetup would require reconfiguring the fixture surface 78 by hand.

As with the dies and molds discussed above, the time required togenerate the required fixture surface 78 with the composite surface 16,based on known dimensional data of the article to be machined, issubstantially less than that required to fabricate a conventionalfixture. As a result, fixtures made according to this invention areeconomically practical to use for prototype or short production rums.

From the above, it is evident that, according to a preferred aspect ofthis invention, the surface generating device 10 can be used to generatea variety of surfaces, each of which can be accurately achieved by theability to appropriately position each of the threaded rods 12 and12a-12e. Depending on the number of threaded rods 12 and 12a-12epositioned, the surface generating device 10 can generate a surface ofwhich at least a portion thereof will conform to at least a portion ofthe contour of an article to be formed or a workpiece to be worked. As aresult, the type of surface features possible with the surfacegenerating device 10 of this invention is only limited by the number anddiameter of the threaded rods 12 and 12a-12e used. For example,generating a very intricate composite surface 16 for a stamping, moldingor die casting operation, in accordance with the first two embodimentsof this invention, generally requires a large number of threaded rods 12having relatively small diameters, so as to enhance the resolution ofthe composite surface 16. In contrast, generating a fixture surface 78for a machining or welding operation, in accordance with the thirdembodiment of this invention, generally requires fewer but largerdiameter threaded rods 12, in that surface uniformity is not a primaryconsideration.

Furthermore, the composite surfaces 16 which can be generated by thesurface generating device 10 of this invention can be done relativelyquickly by assembling the desired number of threaded rods 12, 12a-12ewithin a suitable holding frame 14, and then rotating each threaded rod12, 12a-12e a sufficient number of times to properly longitudinallyposition each threaded rod 12, 12a-12e according to the requirements ofthe particular article being formed or worked. Where an article has beendesigned by computer-aided design and manufacturing methods, thedimensional data produced by such methods can be readily used toautomatically position the threaded rods 12, 12a-12e with an automateddevice such as the automatic screwdriver system 18. Even where anautomated capability is not possible or practicable, the surfacegenerating device 10 of this invention can be readily, and oftenquickly, configured by using conventional handtools. If desired, thefinal surface can be developed by machining or by filling the surface aspreviously described.

Specific advantages associated with using the surface generating device10 as a draw die for a stamping operation include the relatively lowcost of the die 17, as well as the durable materials which can be usedto form the threaded rods 12, such that a die 17 formed with the surfacegenerating device 10 generally has a service life comparable to that ofcast iron dies. Another advantage is that the requirement for a model ofthe article to be stamped is eliminated, in that design data can be useddirectly to properly position the threaded rods 12 so as to achieve thedesired contours on the composite surface 16. Furthermore, surfacedeviations from that which is desired will be known in advance accordingto the known longitudinal position of each threaded rod 12, such thatsubsequent machining operations can be more readily anticipated andefficiently completed. In addition, a metal layer 90 deposited on thedie 17 can be used to further enhance the uniformity of the die surface,so as to further minimize the amount of machining required to bring thearticle within its final design tolerances.

Specific advantages associated with using the surface generating device10 as a mold or die for molding plastics or die casting metals,respectively, also include a relatively low cost, but durable mold ordie which can be quickly generated, so as to eliminate the need formaking patterns to determine the required dimensions of the mold or die.Furthermore, molds and dies formed with the surface generating device 10of this invention can readily be equipped with cooling and heatingpassages 86. Because the passages 86 can be selectively formed byselectively locating the reduced diameter portions 84 on predeterminedthreaded rods 12e, the passages 86 can be customized to vary in size anddistance from the mold or die surface 88, such that the degree ofheating or cooling desired can be achieved. In addition, the cartridgeheaters 92 can be included to further increase the precision in whichthe mold or die surface 88 temperature can be controlled.

Finally, specific advantages associated with using the surfacegenerating device 10 to generate a fixture surface 78 include theability to rapidly develop a fixture off-line which can be specificallyconfigured to support one workpiece, then later reconfigured to supportan entirely different workpiece, eliminating the need for two separatefixtures. As before, if the workpiece has been designed bycomputer-aided design and manufacturing methods, the dimensional dataproduced by such methods can be readily used to position the threadedrods 12a-12d in an automated manner so as to properly support andprovide locating features for the workpiece. As a result, a vastassortment of fixtures need not be stored to accommodate short-run orprototype manufacturing operations. Due to the relatively few threadedrods 12 required to support, locate and clamp a workpiece, the time togenerate the fixture surface 78 is relatively insignificant whencompared to the time to conventionally fabricate a comparable fixture.Furthermore, the degree to which a workpiece is restrained by thefixture surface 78 can be customized to accommodate both thin and weakworkpieces for light machining and large workpieces for rough machining.In addition, several surface generating devices 10 could be gangedtogether to form a larger fixture surface 78, if desired.

It is to be noted that the teachings of this invention could be employedto generate a wide variety of precision surfaces, and not just thestamping, molding, die casting, machining and welding operationsspecifically addressed here. Therefore, while our invention has beendescribed in terms of a preferred embodiment, it is apparent that otherforms could be adopted by one skilled in the art, for example byemploying the surface generating device 10 for other manufacturing orprocessing purposes, or by forming the threaded rods 12 from othermaterials than those suggested here, or by utilizing other methods forrotating the threaded rods 12 to achieve the longitudinal positionswhich generate the desired composite surface 16. Accordingly, the scopeof our invention is to be limited only by the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A fixture for supporting an article having a predetermined contour, the fixture comprising:a structural support member having an interior surface, the interior surface having threads formed thereon; threaded members supported within the structural support member, each of the threaded members having a thread formed thereon, the threaded members being oriented substantially parallel with each other such that adjacent ends of the threaded members define a fixturing surface on one side of the structural support member, the threads formed on each of the threaded members being threadably engaged with the threads of each adjacent threaded member, the threads formed on the threaded members located adjacent the interior surface of the structural support member being threadably engaged with the threads of the interior surface, such that longitudinal positioning of an individual threaded member relative to its adjacent threaded members and the structural support member can be achieved by rotating the individual threaded member; and means adjustably mounted to at least one of the threaded members for locating the article on the fixturing surface; whereby appropriate longitudinally positioning of at least one of the threaded members relative to its respective adjacent threaded members can be performed such that the threaded member supports at least a portion of the article.
 2. A fixture as recited in claim 1 wherein the threaded members are threaded cylindrical rods having male threads formed thereon, and wherein the interior surface of the structural support member has parallel semi-cylindrical channels in which female threads are formed for engaging the male threads of the threaded cylindrical rods located adjacent the interior surface of the structural support member, the threaded cylindrical rods having substantially the same thread pitch and pitch diameter.
 3. A fixture as recited in claim 1 wherein the locating means is threadably mounted within at least one of the threaded members.
 4. A fixture as recited in claim 1 further comprising means mounted to at least one of the threaded members for clamping the article on the fixturing surface.
 5. A fixture as recited in claim 4 wherein the clamping means is an asymmetric clamping means such that rotation of the clamping means provides lateral positioning of the clamping means relative to a corresponding threaded member.
 6. A fixture as recited in claim 1 wherein a plurality of the threaded members are hollow threaded rods having a cavity formed therein.
 7. A fixture as recited in claim 6 further comprising:means mounted within the cavity of at least one of the hollow threaded rods for locating the article on the fixturing surface; and means mounted within the cavity of at least one of the hollow threaded rods for clamping the article on the fixturing surface. 